Field of the Invention
The present application relates to an internal-combustion engine.
Discussion of the Background
An in-cylinder direct-injection internal-combustion engine as an exemplary related art is disclosed by Japanese Patent No. 4054223. This internal-combustion engine includes a piston that reciprocates in a cylinder, and a spark plug and a fuel injection valve that face a combustion chamber provided in the cylinder. The piston has a cavity eccentrically provided in the top surface thereof and extending from a position near the center of the piston to a position near an injection port of the fuel injection valve. The cavity has first and second guiding walls provided near the injection port and near the center of the piston, respectively. The first guiding wall forms a sloping surface extending obliquely and linearly upward from the bottom surface of the cavity in a direction toward the fuel injection valve. The second guiding wall forms another sloping surface extending obliquely and linearly upward from the bottom surface of the cavity in a direction away from the fuel injection valve.
The fuel injection valve is configured to inject fuel mists from the injection port thereof. The fuel mists include a main fuel mist and a sub-fuel mist injected at respectively different predetermined angles. The fuel mists each have a flat shape in side view and a fan shape in plan view. The main fuel mist is injected at a nearly vertical angle and toward a side nearer to the fuel injection valve. The sub-fuel mist is injected at a nearly horizontal angle and toward a side farther from the fuel injection valve.
To cause stratified combustion when, for example, the internal-combustion engine is under a low load and at a low rotational speed, the fuel is injected from the fuel injection valve in the latter stage of the compression stroke. Most of the main fuel mist thus injected is guided along the first guiding wall, whereby a rich air-fuel mixture is produced in the combustion chamber near the injection port of the fuel injection valve. Meanwhile, most of the sub-fuel mist collides with and is guided upward along the second guiding wall, whereby a rich air-fuel mixture is produced in the combustion chamber near the spark plug. The rest of the main fuel mist and the rest of the sub-fuel mist overlap each other and stay in the cavity. Thus, the air-fuel mixture is distributed at a desired concentration in the combustion chamber and, in this state, ignition with a spark plug is initiated, whereby stable combustion is made to occur by flame propagation.